Researchers are always interested in heat generated under dynamically repeated load. In practical application, when various kinds of tire and conveyer belts operate in high speed, internal heat, vibration damping, sound insulation materials and their viscoelasticity damping effect of structure are directed to energy loss analysis caused by hysteresis effect of materials.
When a wheel rotates, the tire is repeatedly compressed and deformed due to a load caused by a partial weight of a vehicle and an impact load of a road surface with respect to the wheel. And the work which is consumed by the compression deformation is mostly converted to heat. Since the materials (rubber, a chemical fiber or the like) of most tires are bad thermal conductors, it is hard to diffuse a quantity of heat. Thus, the internal temperature of a tire body increases rapidly. From the test, we came to a conclusion that the internal temperature of the tire is in direct proportion to the product of a load and a speed of the tire. As the speed increases, the load becomes bigger and the temperature increases more rapidly.
The Goodrich's rubber compression heat-generation test machine applies a certain compression load to a sample through an inert-lever system and applies periodic high-frequency compression with specified amplitude to the sample through a transmission system. The compression fatigue temperature rise and fatigue life of the sample are measured under the condition of a room temperature or a temperature higher than the room temperature within a certain period of time. This is applied to vulcanized rubber having a hardness of 30-85 IRHD.
As illustrated in FIG. 1, according to the principle of a conventional compression heat-generator, a distance from a center line of a sample to a lever supporting point 3 is 127±0.5 mm, and a distance from the center line of a load weight 5 to the lever supporting point 3 is 288±0.5 mm. The sample is guided by an upper pressing plate and is reciprocally compressed under the action of the load, and is heated due to the internal resistance of rubber. The compression load to which the sample is subjected adopts an equilibrium compensation principle of a balance lever and uses a lever balance adjusting device 6 to maintain the balance of the lever. The mechanical model is illustrated in FIG. 2. Since a dimension of the sample is changed due to thermal expansion and contraction, or is permanently deformed due to compression during the testing process, the height of the sample is changed. However, the device cannot record the transient changes in the shape, height and dimension of the sample, and cannot transiently control and maintain the constancy of the static force of the preload. The dynamic force is also affected and fluctuates, causing the data to become more inaccurate and unstable and the repeatability becoming relatively poor as the test is performed. Furthermore, a frequency (rotating speed adjustment) of the conventional compression heat-generator and a test temperature are all fixed in a single manner. The dynamic strain of the sample (i.e., a stroke of the upper pressing plate) is also fixed. Accordingly, the compression heat-generation test cannot be performed under the condition of different frequency, temperature and dynamic strain, and it has a single function.
The heat-generator in the current market has several disadvantages as follows.
1. As illustrated in FIG. 3, since the lever supporting point and the sample supporting point are not superimposed on the lower surface of the balance lever equilibrium compensation sample, when the weight difference between the front weight and the back weight causes the lever to be inclined at an angle α, the lower surface of the sample and the upper surface to which the pressure is applied will not be parallel, and it will have a deviation from the model in which the wheels withstand the gravity of a vehicle body and periodically withstand the compression of the vehicle body. Therefore, the actual working condition cannot be accurately simulated under the test condition.
2. The compensation value is not accurate. The compression is in a vertical direction while the compensation is in an inclined direction. Likewise, as illustrated in FIG. 3, the compression applied by the rubber sample is in the vertical direction, while the compensation caused by the lever is in the inclined direction, so that the angle α is formed between compensation direction and vertical compression direction.
3. A central temperature of a core portion cannot be measured in real time. The central temperature of the core portion is actually reflected by a quantity of heat generated by the repeated compression of the rubber material. However, what can be measured in real time in the current market is basically the temperature of the internal environment of the device or a temperature of the sample surface (e.g., bottom). The central temperature of the core portion of the sample can be measured only after stopping a compression test. However, at this time, when a needle-shaped temperature sensor is inserted into the rubber sample, a difference between its temperature and an actual internal temperature of the sample is relatively large. Accordingly, an error occurs in the test result.
4. The device is configured to measure a temperature of only one sample temperature.
5. Some manufacturers can also use a method wherein the internal temperature of a sample can be measured in real time, and usually a temperature measuring wire is inserted by perforating a central position of the sample, or the temperature measuring wire is vulcanized into the central position of the sample when manufacturing the sample. As illustrated in FIG. 4, when the sample is perforated, if the hole is too small, the temperature measuring wire is relatively soft so that it cannot be inserted into the hole. If the hole is too large, the sample may burst during the compression process. At the same time, during the testing process, due to high frequency vibration, deformation of the sample, or the like, the temperature measuring wire may also be separated from the sample and be located off the center position so that the central temperature of the core portion cannot be reflected accurately. When the temperature measuring wire 1 is vulcanized into the test sample, it also cannot be guaranteed that a temperature measuring point is always at the center position of the sample during the vulcanization process.
6. At present, a compression heat-generator manufactured by Ueshima Company in Japan can measure the central temperature of a core portion of a sample in real time. According to a specific method, the device includes one set of temperature sensor inserting units. A needle-shaped temperature sensor can be vertically inserted from the top of a rubber sample into an internal center position of the sample. An inserting depth of the temperature sensor can be controlled by a computer based on feedback information. Before starting the test, the needle-shaped temperature sensor is inserted from the top of the sample into the center position of the sample. During the testing process, a height of the sample is changed according to time and the measured value based on the height changes is fed back to the computer. The inserting position of the needle-shaped temperature sensor can be adjusted to always be located in the center position of the sample by controlling the operation of the temperature sensor inserting unit through the computer. Since this method has a complicated structure and there is a friction phenomenon existing between a probe of the temperature sensor and the rubber sample during the compression process, reliability and operability of the device and accuracy of the test results are affected.